1. Field of the Invention
The present invention relates generally to polymeric materials which are suitable for high temperature applications as a result of this high thermooxidative stability. It relates particularly to a series of polyimides based on aromatic diamines with a pendant trifluoromethyl grouping.
2. Description of Related Art
Polyimides are an important class of polymers for high temperature applications due to their high thermooxidative stability. One monomer of major importance in preparing these high temperature polyimides is 1,3-phenylenediamine (m-PDA). 3,5-Diaminobenzotrifluoride (DABTF), a reported diamine (R. A. Henry, D. W. Moore and R. L. Atkins, J. Heterocyclic Chem., 13, 375 (1976).), is an analog of m-PDA and contains a symmetrically, substituted polar CF.sub.3 group. Diamines and dianhydrides containing two or more of these trifluoride groups such as 2,2-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride (6FDA), 2,2-bis(3-aminophenyl)hexa-fluoropropane, (6F) 2,2-bis[4-(4-aminophenoxy)phenyl]hexafluoropropane (4-BDAF), and 2,2-bis[4-(3,4-dicarboxyphenoxy)phenyl]hexafluoropropane dianhydride (BFDA) are known in the polyimide literature. (D. L. Goff and E. L. Yuan, Polymeric Materials Science and Eng., Preprints 59, 186 (1988). G. R. Husk, P. E. Cassidy and K. L. Gebert, Macromolecules 21, 1234-1238 (1988). T. L. St. Clair, A. K. St. Clair and E. N. Smith, Structure-Solubility Relationships in Polymers, Academic Press, Inc. New York, N.Y. 199-214 (1977).) ##STR2##
An object of the present invention is to provide a polyimide based on DABTF that provides high molecular weight poly(amic acid) solutions that yield creasable free-standing films and coatings in the fully cured form.
Another object of the present invention is to provide fully cured polyimide films based on DABTF with enhanced solubility in common organic solvents such as methylene chloride, N,N-dimethylacetamide (DMAc) and m-cresol.
Another object is to provide a polyimide composition based on DABTF which exhibits a lowered dielectric constant, compared to state-of-the-art polyimides, in the range of 2.5 to 3.0 at 10 GHz.
Another object is to provide a high temperature aromatic polyimide prepared from DABTF which exhibits improved optical transparency, compared to state-of-the-art polyimides.
A further object is to provide polyimides based on DABTF that form well-consolidated moldings.
Another object is to provide a polyimide based on 4-trifluoromethyl-2,6-diaminopyridine and 6FDA that has a high level of fluorine atoms per repeat unit.
Another object is to provide a polyimide with pendant trifluoromethyl groups that contains a nonbenzenoid aromatic moiety.